Question

I have the following code. Will it be thread safe even if the set itself is not thread safe?

private ConcurrentMap<REGISTRY, Set<CONTACT_ROLES>> proxyRoles = new ConcurrentHashMap<REGISTRY, Set<CONTACT_ROLES>>(); 


    public void setProxyRoles(ConcurrentMap<REGISTRY, Set<CONTACT_ROLES>> proxyRoles) {
        this.proxyRoles = proxyRoles;
    }

    public ConcurrentMap<REGISTRY, Set<CONTACT_ROLES>> getProxyRoles() {
        return proxyRoles;
    }

    public synchronized void addProxyRole(REGISTRY reg, CONTACT_ROLES role) {
        if(proxyRoles.get(reg) == null){
            proxyRoles.put(reg, new HashSet<CONTACT_ROLES>());
        }
        proxyRoles.get(reg).add(role);

    }

EDIT:

After some very good answers I understand that my solution would not be safe and I googled a bit and found a good replacement for my set in a ConcurrentSkipListSet

Answer 1

From Javadoc:

A hash table supporting full concurrency of retrievals and adjustable
expected concurrency for updates. This class obeys the same functional
specification as Hashtable, and includes versions of methods
corresponding to each method of Hashtable. However, even though all
operations are thread-safe, retrieval operations do not entail
locking, and there is not any support for locking the entire table in
a way that prevents all access.

So if 2 threads are accessing the set simultaneously, they won’t acquire lock on entire set.